Waterproofing with Alum

**Stovemandan** · 10-27-2013, 17:06

I have a very large piece of ripstop nylon that I want to waterproof by submersion. Has anyone ever used this method:

1. Mix 1 pound (0.45 kg) of laundry detergent with 2 gallons (7.5 L) of hot water in a large container. You want the container to be large enough so that you can soak all of your fabric in the detergent mixture.

2. Soak the fabric in the mixture until it is completely saturated. Hang the fabric to air-dry in the sun.

3 Combine 1/2 pound (0.25 kg) of alum with 2 gallons (7.5 L) of hot water in a second container. After the fabric has dried out from the laundry detergent soak, steep the fabric in this mixture for at least 2 hours.

4 Hang the fabric in the sun to air-dry completely.

**DuctTape** · 10-27-2013, 18:21

I have read about it, but never tried it.

**hk2001** · 10-27-2013, 18:29

I've only seen Alum used to cure skins.

Can it seriously be used to waterproof?

**DuctTape** · 10-27-2013, 19:57

George Washington Sears aka "Nessmuk" used alum to waterproof cotton canvas.

"To 10 quarts of water add 10 ounces of lime and 4 ounces of alum; let it stand until clear; fold the cloth snugly and put it in another vessel, pour the solution on it, let it soak for 12 hours; then rinse in luke-warm rain water, stretch and dry in the sun and the shanty-tent is ready for use."

**nothermark** · 10-27-2013, 20:35

There are a lot of references to various alum compounds for waterproofing cotton. Cotton swells when wet helping to close the pores in the weave. Nylon stretches thus opening up plus I question how well it wets out compared to cotton. I would try a large scrap and see what happens before I committed the material for a tarp.

**Stovemandan** · 10-27-2013, 21:26

Thanks everyone for your comments.

I suspect the lime in the formula used by Nessmuk serves the same purpose as the clothes washing soap in the formula that I have in the formula I found on the net. It's a mesh prep of a type, removes lubricants used on threads during weaving process.

In my reading today I came across a site that said alum was used for backpacks and other sports products.

One of the other uses of the alum was for fire retardant for fabrics........I like multi use

**pndwind** · 10-27-2013, 21:38

If it doesn't waterproof nylon you can always make pickles

.

**psyon27** · 10-29-2013, 02:10

Or use it after shaving. It may sting if you cut yourself but it will slow bleeding, prevent infection, and tighten your skin.

**Stovemandan** · 10-29-2013, 08:26

Or I can use as a means of water purification. Gee , this alum stuff sure is multi-purpose.

I will be using it to treat my ripstop fabric as soon as the weather permits. I'll be using food grade pickling lime and detergent that comes in a box, not bottle.